There are a variety of thermal transfer methods using thermal transfer sheets made by forming color transfer layers on base sheets. The color transfer layers of the thermal transfer sheets are heated from behind the thermal transfer sheets with a thermal head or the like in patterns for yellow, magenta and cyan images of characters, figures or patterns, respectively, and the patterned yellow, magenta and cyan layers are transferred to the surface of a transfer recording medium. Thermal transfer methods are classified roughly by the type of the color transfer layers into those of the sublimation transfer system and those of the melt transfer system. The thermal transfer method of the sublimation transfer system uses thermal transfer sheets made by forming color transfer layers each of a binder containing a dye that sublimates or shifts when heated on base sheets, heats the thermal transfer sheets from behind to make the dyes contained in the color transfer layers transfer from the thermal transfer sheets to a recording medium. The surface of the recording medium is coated with a recording layer that can easily be dyed.
The thermal transfer method of the melt transfer system uses thermal transfer sheets made by forming color transfer layers that soften, melt and become transferable when heated on base sheets, heats the thermal transfer sheets from behind to transfer the color transfer layers to the surface of a recording medium. Both the thermal transfer methods of the sublimation transfer system and those of the melt transfer system are capable of forming monochromatic images and multicolor images. In forming a multicolor image, the thermal transfer method uses three or four color thermal transfer sheets for, for example, yellow, magenta and cyan images or, when necessary, yellow, magenta, cyan and black images, and thermally transfers the color images of those colors to a recording medium to form color images.
The thermal transfer method holds a plurality of thermal transfer recording sheets in a stack and feeds the thermal transfer recording sheets to a printer or uses a thermal transfer recording web roll and feeds the thermal transfer recording web to a printer.
Recently, the thermal transfer method is used for the thermal transfer recording of a large amount of prints, and thermal transfer recording web rolls are used. The thermal transfer recording web roll, in general, is formed by winding a thermal transfer recording web around a feed core (bobbin). The leading edge of the recording web wound around the feed core is attached adhesively to a take-up core and is taken upon the take-up core after the completion of thermal transfer recording or the recording web is cut in a sheet after the completion of thermal transfer recording and the printed recording sheet is delivered.
The aforesaid conventional thermal transfer recording web roll has the following problems.
(1) The conventional thermal transfer recording web roll needs a feed core formed in a high dimensional accuracy to roll the thermal transfer recording web uniformly around the feed core without creasing the thermal transfer recording web. Thus, the feed core is inevitably costly.
A feed core of a reduced cost may be a paper tube formed mainly of paper pulp instead of a plastic material. The paper tube is brought into contact with a driving member of a printer to rotate the thermal transfer recording web roll on the printer. Paper powder is produced due to the abrasion of the paper tube by the driving member in rotating the thermal transfer recording web roll, the paper powder scatters in the printer and, consequently, pinholes are formed in prints formed by thermal transfer printing deteriorating image quality.
(2) The core is mere waste after the thermal transfer recording web held thereon has been used up. Since the cylindrical core is bulky for its weight, the core cannot efficiently be carried for waste disposal. The core is not recycled and thrown away, which is against demand for waste reduction to avoid environmental problems.
(3) It takes time and requires troublesome work to store cores, to set a core on a take-up machine for taking up a thermal transfer recording web and to wind a thermal transfer recording web around the core.
(4) An end part of a thermal transfer recording web cannot correctly attached to a desired part of a core in attaching the end part to the core with an adhesive tape, an adhesive double-coated tape or a paste. The thermal transfer recording web meanders while the same is being wound round the core and, consequently, the width of a thermal transfer recording web roll formed on the core is somewhat greater than that of the thermal transfer recording web. Since the thermal transfer recording web is wound under a specified tension and a specified pressure around a hard, cylindrical core, the position of the thermal transfer recording web roll formed on the core cannot be adjusted relative to the core. Therefore, the core must have a length greater than the width of the thermal transfer sheet taking into consideration the attachment of the end part of the thermal transfer recording web to an incorrect part of the core, and the formation of a thermal transfer recording web roll having a width greater than the width of the thermal transfer recording web. Thus, the thermal transfer recording web roll formed by winding a thermal transfer recording web around a core is inevitably large.
Sometimes, the thermal transfer recording web roll is deformed when shocks act on the thermal transfer recording web roll when the thermal transfer recording web roll is dropped or handled improperly in carrying the thermal transfer recording web roll or loading the thermal transfer recording web roll into a printer. It is difficult to straighten the deformed, hard thermal transfer recording web roll.
The incorrect winding of the thermal transfer recording web around the core and the deformation of the thermal transfer recording web roll while the thermal transfer recording web roll is handled affect adversely to the accuracy of print position on the thermal transfer recording web.
(5) Flaws corresponding to steps including an end part of the thermal transfer recording web attached to the core and an end detection hole formed in the thermal transfer recording web are formed in the thermal transfer recording web roll due to pressure and tension that act on the thermal transfer recording web, and the flaws become apparent in different densities of prints. FIG. 10 is a view of assistance in explaining the formation of flaws in a thermal transfer recording web 10a. In FIG. 10 flaws 3 due to an end indicating hole 2 and an end part of the thermal transfer recording web attached to a core 1. Sometimes, the hardness of the thermal transfer recording web roll is reduced by adjusting winding tension and winding pressure to prevent the foregoing problem due to the adverse effect of the end part of the thermal transfer recording web attached to the core and the end detecting hole on prints, which, however, could not achieve a desired effect.